Abstract: The residual water content of soil rock mixture plays an important role in the study of soil water characteristics,seepage and disaster mechanism in Qinba Mountain area. To study the correlation between the residual water content and its microstructure characteristics of soil rock mixture which widely distributed,the air-dried and mercury intrusion method were introduced to obtain the residual water content and pore distribution of soil rock mixture under different void ratio and rock content conditions. The research shows that the void ratio,rock content and residual water content of soil rock mixture have negative correlation at confidence 99.5%. Residual water rate of soil rock mixture is related to internal pores of aggregates(<2 μm),and the residual water content is mainly exits in pores less than 0.5 μm. Under the condition of the same stone content,reducing the pore ratio makes the pore distribution shift to the direction of small pores,which increase the content of small pores content and the residual water content. The rock content affects the internal pores of the aggregate in soil rock mixture by affecting the clay matrix content and the deformation degree of the clay matrix in the soil rock mixture,thus affecting the residual water content. Based on the analysis of the influence mechanism of porosity and rock content on the residual water content of soil rock mixture,a model for predicting the residual water content of soil rock mixture in Qinba Mountain area based on rock content and pore ratio is proposed. The comparative study shows that the proposed model could predict the residual water content of soil rock mixture well with specific structure in Qinba Mountain area.